Keep Losing Prime - PeachParts Mercedes-Benz Forum

legasea · #1 04-13-2010, 10:08 PM

A couple weeks ago I ran out of fuel in my 83 300D turbo. After filling with diesel and pressing the primer 100 times (new style), it finally started and ran well. I was still seeing bubbles in the return line but ran fine. Ever since then, the only way it will start is if I prime it. When I lift up the hood, I see there is no fuel in the diesel return line (clear lines). After starting, I will always see bubbles. I tightened all the hose clamps on the lines and fuel filters. What could be causing it to lose prime everyday? Runs great after priming. BTW, this is also a WVO conversion - custom kit. Runs fine on oil too once warm.

layback40 · #2 04-13-2010, 10:15 PM

You may have crap in the lift pump valves.

Diesel911 · #3 04-14-2010, 12:16 PM

Air leak or Lift Pump issue.

Replacing Hoses does not cost much and taking the lift pump apart is time consuming but not difficult. The big Plug on the side of the lift Pump is 30mm.

legasea · #4 04-20-2010, 09:16 PM

All the hoses from engine to tank are all new with a newer primer pump. I also just went through all hoses and retightened all hose clamps. Can't find this darned air leak. Could the primer be bad already? Can someone share the steps to remove the fuel pump and rebuild (if possible). Maybe a leaky oring or gasket on the pump?

layback40 · #5 04-20-2010, 09:55 PM

Maybe a leak in your WVO system. if you place the car facing down hill does the problem still occur?

dieseldan44 · #6 04-20-2010, 10:20 PM

how is your WVO system configured?

is the diesel secondary filter housing now under vacuum?

if thats the case, the rubber o-rings on the fuel filter spin on bolt are likely culprits.

dont go tearing the fuel pump apart yet IMHO.

legasea · #7 04-21-2010, 09:53 AM

Attached is an image of my WVO design.

dieseldan44 · #8 04-21-2010, 10:46 AM

Yea, your diesel side is under vacuum from the fuel pump.

Have you had this issue only since installing your conversion?

legasea · #9 04-21-2010, 02:25 PM

No, I installed the conversion about 2 yrs ago and it has been running fine on oil and diesel since then. This just started out of the blue. I am due to change the spin on fuel filter anyway and I will try to tighten down the primer as well to see if either of those two things help.

dieseldan44 · #10 04-22-2010, 12:11 AM

I am having / had the same problem as you, just not as severe....with the same sort of maddening results and mysterious-ness.

Check out this thread about it on the Frybrid forum:
http://www.frybrid.com/forum/showthread.php?t=15778

Parking the nose of the car downhill and looking for fuel leaks is a good method, especially in your situation where the leak is severe. (its suggested in the frybrid thread)

Check the return lines too - I think they can cause you to lose prime if they're loose.

Pics of your setup?

legasea · #11 04-22-2010, 09:44 AM

Excellent thread to troubleshoot leaks. I have a few things I can check now. This is my blog of the whole design.....had to separate it into a couple posts here to fit it.

My goal with this blog is to fully document the waste vegetable oil (WVO) conversion that I have installed on my 1983 300D Turbo Benz. After months of learning about these conversions in the online forums, I set out to design my own kit and have purchased all the parts online from different suppliers. There were a few pre-built kits out there that I was considering (Greasecar and Frybrid), but I decided to buy most of my parts from PlantDrive.com.
I worked with Craig Reece over at PlantDrive and purchased their TTVTS package that I built the rest of my conversion kit around. I highly recommend customizing your own kit specific to your car and climate. I also recommend picking a parts supplier that is not only easy to work with and available to help with your design, but a vendor who stands behind their products is also very important. That is what led me to PlantDrive.com. Below are the parts I have used. You can click on each part to view an image.
WVO Conversion Hardware:

Step by Step Conversion

1. Design: The first step, even before buying any parts, is to design your conversion kit on paper taking into consideration the type of diesel vehicle you have and what climate you live in. If you live in warm climates that don’t get below 50 degrees fahrenheit, your system will require less heating parts than someone living in colder climates. Once you know how your existing diesel fuel system works, you will know what parts you need to purchase. Then you can design on paper the flow of your existing diesel fuel and add the new veggie oil fuel flow. One of the more important decisions is knowing how you want to plumb the return lines for both veggie oil and diesel fuels. I will go into more detail about this later.

CLICK HERE FOR MY WVO DESIGN DIAGRAM

2. Order: Now that you have all your parts detailed in your design diagram, you can begin to source quality parts online and at your local suppliers. Be sure that some or all of your parts come with at least a 1 year warranty.
3. Layout: Once all of your parts have arrived, you will start by dry fitting the components, starting with the tank and work your way forward. You will lay out the hoses and hardware making sure that the flow does not interfere with any moving parts and the hood can close with a little clearance. Take note where you will tap into your coolant and where your existing fuel supply and return lines are. If you will be running bio-diesel in your primary tank, used to start and stop the car, you will want to replace all your existing supply and return lines with viton or another similar hose.
As you are dry fitting the components, you will want to also take this time to figure out where you will tap into the coolant supply and return lines. On the MB you want to tap

into the heater hose where it emerges from the head which is between the head and where the heater hose enters the firewall/bulkhead right behind the oil filter. A decision will be made to run the coolant in series or parallel. You want to use parallel for any vehicle where coolant only flows thru the heater core when the cabin heater is turned on. You can’t use a series connection in these vehicles, because then the WVO system will not get any hot coolant unless the cabin heater is turned on and if the cabin heater is turned on, it

will take most of the heat out of the coolant for a long time, and you’ll have very long switchover times anyway. For parallel, you will tee into the coolant supply line going to the heater core and then run from that tee to supply the WVO system. You tee into the coolant return line coming from the heater core. Then into that tee to accept the return from the WVO system. More specifically, you install a 5/8 X 5/8 X 3/8 tee into the supply hose, and that’s your coolant supply. For your

return tee, you need to install it *after* the small 12V circulation pump and before the waterpump. If you install it before the 12V pump, you’ll only get circulation when the heater is on. Usually this hose is 5/8″ ID also, but sometimes it’s 3/4″ - so check. This description of coolant lines and photos are from Dana Linscott’s veggie forum.

legasea · #12 04-22-2010, 09:45 AM

4. Tank: After you have a good idea where everything will go, it is time for assembly. If possible, mount the tank in such a way that you either have full access to the spare tire or in such a way that it is relatively easy to unmount the tire (w/o tools) in the event you need to get to the spare. I opted to go with the 20 gallon Trekker tank with a coolant heated aluminum heat exchanger. This can be had for about $500. The Trekker tank also came with an electronic fuel gauge with sending unit. The sending unit was already mounted in the tank. I ran a 12 gauge wire from the tank, through the back seat, under the carpet and up behind the steering wheel. I made the connections to the back of the fuel gauge and mounted it. An alternative is to get yourself a marine Temp tank but make sure it is baffled to minimize oil from sloshing around and made from cross-linked polyethylene or aluminum. You will also need a remote fuel gauge, sending unit and a way to heat the oil. This can be accomplished with a stainless steel, coolant heated Hotfox mounted horizontally.
5. Tank Heater: Once the tank is mounted, you will then begin connecting the coolant

and fuel lines to the in-tank heat exchanger. Make sure to coat all threaded fittings with Permatex High Performance thread sealant or an equivalent sealant. Be sure not to coat the first set of threads with any sealant and do not use teflon tape. It is better to error on the small size for the hose-to-fitting connections rather than depend on the clamp for all the sealing power. As the filters become used and collect debris, the vacuum will become greater putting additional strain on the fittings. This is the primary area where air can enter the lines.
6. HOH: Next you will run the coolant and fuel lines through a hole in the trunk, along the undercarriage and back up to the engine compartment. The coolant return line will branch off to the passenger side of the engine to the coolant return tee. The WVO fuel supply line and the coolant supply line will branch off to the driver side of the engine. Once these lines are ran and connected to the respective components, you will go back to insulate and secure the hose-on-hose (HOH) fuel/coolant bundle. This can be done with a combination of standard pipe insulation or reflective pipe wrap, foil tape, heavy duty zip ties and rubber p-clamps.
The idea is that the heat from the coolant will warm the oil in the fuel lines enough to keep the oil flowing. An alternative way to plumb the coolant and fuel lines is to use hose-in-hose (HIH). This is done with a 5/8″or larger coolant line and an aluminum fuel line that runs inside the coolant line. The major disadvantage of this design is that if a leak exists and you do not see it, it will allow coolant to get in the fuel lines and fuel to get in the coolant lines. Both of these scenarios is something you want to avoid. The benefit of HIH is that it is more efficient at heating up the oil as it travels from the tank to engine. HOH has proved to be sufficient at this task and is a much safer means to plumb the lines…..no worries.
7. FPHE: Next we will connect the fuel and coolant to the flat plate heat exchanger (FPHE). Be sure to mount your FPHE in the vertical position and pay special attention to the flow. The two fluids (oil and coolant) are plumbed in a counterflow direction. This is critical to the proper operation and heating of the FPHE. The FPHE will have four

ports, two for coolant and two for oil. They are labeled A1, A2 for coolant and B1, B2 for oil.
To plumb in a counterflow direction, from the coolant supply tee, connect coolant supply line-in to A1 and coolant supply line-out to A2. Then connect the WVO supply line-in coming from the tank to B2 and WVO supply line-out to B1. Again, use Permatex High Temperature thread sealant on all four connections and be generous with the stuff. Once completed, insulating the FPHE is recommended for maximum efficiency. It is important to follow the instructions on the thread sealant box for curing times. There is normally a 2-4 hr window where you can move the fittings. After 24 - 48 hrs (sometimes 72 hrs), if you unscrew the fitting, you will have to replace the fitting and reinstall.
8. Vegmax: The next component in our coolant/oil flow is the Vegmax coolant heated oil filter. I have seen others coil coolant line around a standard fuel filter to heat the oil and there are also electric type of filter heaters. I went with the Vegmax for a couple reasons. First off I knew I wanted a coolant heated filter, partially because I already invested in a Vegtherm electric inline heater downline of the filter. Another reason is because the Vegmax has a patented aquabloc water separating filter. Water is dispelled from the oil and can be drained off at the bottom of the filter.
Before mounting the Vegmax filter, remove thefilter media which will be filled with clean oil later on before it is screwed back on. Make sure it absorbs the oil as much as possible to help minimize purging air later on. Once you

have found a good location for the filter, make sure you have access to the drain on the bottom and plenty of clearance when the hood is closed.After it is mounted, connect the WVO supply line from the FPHE to the fuel-in port and then continue the fuel supply line on the fuel-out port. Then connect the coolant lines. There are not specific supply and return lines for the coolant. Take the coolant supply line coming out of the FPHE and connect to the Vegmax. Continue the coolant supply coming out of the Vegmax to the fuel tank coolant-in port on the heat exchanger. Use Permatex High Temperature thread sealant on all four connections. Another good idea is to insulate the Vegmax filter. This can be done with a variety of products, but a bottle cozy works nicely.

legasea · #13 04-22-2010, 09:46 AM

9. Supply Valve: The supply valve will need to be installed as close to the fuel injection pump as possible to minimize purge times. Before connecting the Hydroforce 12 volt fuel supply valve, I will install a brass T fitting that will be used to loop the fuel return line. 4″ - 6″ or so after the Vegmax, splice in the brass T fitting. Then 4″ - 6″ after the T fitting, you will connect the fuel line to the supply valve “normally closed” port. This is the port that is closed when no power is supplied to the valve (in the off/diesel position). On the other end of the valve you will continue the fuel line coming out of the “common” port. This is the port that is always open in either switched position.
Next take the stock diesel fuel line apart where it connects to the lift pump. The is right after the clear inline diesel fuel filter. Leaving the filter inline, connect this line to the “normally open” port on the supply valve. This is the port that is open when no power is supplied to the valve so that when you start your car and the fuel switch is off, diesel will flow through the valve.

10. Vegtherm: Continue the fuel line that comes out of the supply valve (common port) and connect it to the Vegtherm. For this length of fuel hose, it is important to use SAE J30R9 high pressure fuel injection line. Use the same fuel line on the other end of the Vegtherm to the sight glass fuel-in port. Then from the sight glass fuel-out port connect to the stock lift pump using J30R9 fuel line. For the electrical connections, I will use a separate SP/ST “single throw/single post” switch. I can also share the WVO fuel switch so that when I switch over to WVO, the
Vegtherm will turn on, but then when the car is up to temperature, in the summer or in traffic when the oil is hot, I will not be able to shut off the Vegtherm. Wiring a separate switch for the Vegtherm gives me full control over the heat. The Vegtherm was designed to heat the fuel and maintain a temperature of 158 F (70 C) if used with a looped return line. It runs at an average amperage draw of 16 - 22 amps designed for the Benz stock 55 amp alternator. Do not insulate the Vegtherm. As a precaution, I will also install a Vegsensor which will automatically shutoff the Vegtherm if temps reach in excess of 212 F (100 C). A suitable mounting location on the Benz is on the fuel injection hardlines using rubber P clamps.
Relay Terminal Numbering Schema

* 30 - Main Power from 12V power supply via circuit breaker
* 85 - To chassis ground
* 86 - “Trigger” from a switched power source
* 87 - Power to 10 gauge red wire on Vegtherm
First mount the relay on the firewall. Then mount the circuit breaker on the firewall close to the battery. Next run a red 10 gauge wire from the + battery terminal to the positive on the battery side of the circuit breaker. From the auxilary side of the circut breaker, run red 10 gauge wire to the #30 terminal on relay. Then connect the red wire on the Vegtherm to the #87 terminal on the relay. Connect the ground wire from the relay and from the Vegtherm to a secure ground on the firewall. Now run the trigger wire #86 in through the firewall into the cabin to the toggle switch at the WVO Control Panel. Then connect a 10 gauge wire to a fuse in the fuse box which is only powered with the key is turned. I have used the rear defroster fuse. From this fuse, run the wire through the firewall into the car towards the ashtray which will be the location of the WVO Control Panel.
What this will do is prevent an accident waiting to happen. If for some reason, the car is shutoff with the Vegtherm toggle switch in the “powered” position, the Vegtherm will be shutoff because it is on the same line as the rear defroster. This can be tested with a test light before and after any connections are made. To make the connection more secure at the fuse box, it is best to solder the wire into place. Finally connect the two wires coming into the car to the switch at the WVO Control Panel and label it VT or Vegtherm. Use wire ties to fasten any loose wires away from any moving parts and heated objects.

11. Vegsensor: The Vegsensor is used to prevent the fuel oil from reaching temps in excess of 212F (100 C). The Vegsensor wire is installed inline of the switched power line coming off the #86 terminal. The actual sensor is clamped to the inlet side of the Vegtherm on the white rubber sleeve. If the Vegstherm is shutting off too early, move the sensor downline in the direction of the tank.
12. Return Valve: The return line will be used with a loop when switched to WVO. To start, locate and disconnect the return “cigar” hose. Connect a new return line (SAE J30R9) from the spin-on fuel filter to the “common” port of the 12 volt Hydroforce return valve. Next connect fuel line from the “normally open” port on the return valve to the diesel return hardline. This line can be either SAE J30R9 or SAE J30R7. I have chosen to use translucent polyurethane fuel line rated for bio-diesel. This will allow me to see if there is any air in the system. Next connect fuel line from the “normally closed” port on the return valve to the brass tee that was installed right before the supply valve. Again, I chose to use the transparent line here.
13. Banjo Bolt: At this point, it is necessary to plug the banjo bolt located on top of the

spin-on fuel filter to prevent WVO from returning to the diesel tank unnecessarily. For this task I used JB Weld and plugged the bottom of the bolt. When it cured, I filed the bolt smooth and flush then reinstalled. Follow the instructions closely on the box for mixing and curing times. There is a dye test that can be used to check for cross contamination of diesel/oil fuels. This dye can also be used in conjunction with a sight glass to determine how long you will need to run in purge mode before turning off the engine.
14. Temp Gauge: The oil temperature gauge was mounted in the WVO Control Panel which used to be my stock Benz ash tray. I cut out two 2″ holes for both gauges. I installed the temp gauge sending unit after the Vegtherm and before the stock lift pump. A single 12 gauge wire is ran from the sending unit, through the firewall and towards the WVO Control Panel. Power and Ground wires were also run to complete the connections. I spliced into the same switched power as I did with the Vegtherm. All connections on the back of the gauge were completed and the gauge was mounted.
15. Vacuum Gauge: The Vacuum/Pressure gauge was installed in a similar manner. I installed the vacuum sending unit after the Vegmax and before the supply valve. This will give an accurate reading and let me know when to change my WVO fuel filter in the Vegmax. A sending tube (fragile) was ran from the sending unit through the firewall towards the WVO Control Panel. Power and Ground wires were also run to complete the connections. I spliced into the same switched power as I did with the Vegtherm. All connections on the back of the gauge were completed and the gauge was mounted.
16. WVO Control Panel: Modifying the stock ash tray was a precise job with much care taken not to destroy the

thin wood panel. Along with the two gauges already described, I mounted three single pole/single throw lighted switches. The green switch is for the Supply Valve, The yellow switch is for the Return Valve and the red switch is for the Vegtherm. I once again spliced into the same switched power source as I did for the Vegtherm. Separating the switches gives me full control of the purge cycle and the heat supplied from the Vegtherm. In the summer months sitting in traffic, it is likely that the Vegtherm will create too much heat. The separate switch will allow me to shut it down if I see the temperature is too high. Wiring all these switches into the switched power source will also shut down the Vegtherm and both valves if I forget to purge when I shut the car off.

legasea · #14 04-22-2010, 09:46 AM

17. Insulation: Once all the fuel and coolant hoses were ran and secured, I went back through and covered all the

lines with foil insulation. I used foil tape and zip ties to secure the insulation to the stock fuel hard lines. I also insulated part of the lines under the hood and in the trunk. Take care not to tighten down too hard if securing to the stock fuel lines. Mine were rusty near the trunk and I tightened too hard. This caused the stock supply line to crack and leak. I had to run a new diesel fuel supply line from the diesel tank to the engine. I attached the new diesel line to the insulated hose-on-hose bundle.
18. Purge: Once all the hardware has been installed, it is time to purge the coolant and the new fuel line. To purge the coolant line, I inserted a drill pump inline of the coolant supply line. I turned on the drill pump and allowed the coolant to flow through the new lines. I also connected the mityvac to the discharge line going to the coolant overflow bottle. After doing this, I had to add 1 gallon of new coolant. Taking the car for a test drive allowed the coolant circulation pump to purge the rest of the air. I then topped off the coolant a bit more and tested that all the coolant heated hardware was hot. I then checked for leaks and tightened a few clamps. Now she is leak free!
For the oil, I used the mityvac pump and connected it to the new fuel line right before the lift pump. I switched on the fuel supply valve and the return valve and pumped away until oil began to flow through the mityvac. I then switched off both valves to pump through the diesel. I then connected the fuel line back to the lift pump and pumped the primer bulb about 50 times.
19. Test Run: For my first test run I got the car up to temperatur at 80 degrees celcius. I then turned on the vegtherm inline heater for 1 minute to allow it to also get up to temperature. I then switched the WVO Supply Valve on for 15 seconds, then back off to let the diesel flow again. I then switched back to WVO for 30 seconds and back to diesel. I did this one more time then finally left it on WVO and also turned on the return valve to allow the WVO to loop back to the supply valve. I ran the car for 10 minutes around town and got out to smell my exhaust……smelled delicious. I then switched all valves and the vegtherm off to purge the system for 5 minutes. I did not notice any interruption in fuel flow due to the proper amount of priming prior to final assembly. If you prime both the diesel and WVO 100%, you will have a successful initial switchover.
20. Once Over: Go over all connections, both coolant and fuel and tighten all hose connections. Periodically, check all systems including the HOH under the car as well as the Trekker tank in the trunk.

dieseldan44 · #15 04-22-2010, 10:01 AM

Nice work...I appreciate all the thought put into that. I bought a Frybrid kit as my base and modded on top of that...so much respect for all your customization.

I need to document mine like that as well. I just have one tiny diesel side air leak thats preventing this from being done.

Do you get any air bubbles/stalling when you purge and go back to the diesel side?